Thermosetting resins. As part of polymeric materials, crosslinked glassy those arising from in situ polymerization of liquid, or easily liquefiable hot-oligomers and / or other low molecular weight organic compounds chemically reactive multi-functional initiators + and / or catalysts (resin thermosetting) play a key role for decades for a myriad of industrial, civil and military.

Despite the growing environmental and ecological pressures of the last 10-15 years the use of thermoplastic polymer materials (especially in the areas of consumer products such as automotive, rail, industrial vehicles and civil construction) because of their (at least potentially easier) recyclability, thermosetting resins are, thanks to their insolubility infusibility and objective and that poses severe obstacles to the common and convenient procedures for reprocessing hot material still irreplaceable in a variety of skilled employment:

as matrices of structural composites and semi-lightweight structural (inclusive high volume fractions of fiber reinforced high modulus);

electroinsulating and dielectric materials as for electro-mechanical devices and electrical power at medium and high voltages;

as matrices of composite materials for printed circuits;

as materials for protective coatings (in particular, anti-corrosion) of metal surfaces. Moreover, they represent an important component of the stones for sharpening, the binder that holds the abrasive, typically aluminum oxide. Although a full spectrum of chemical-physical and physical-mechanical qualifications in relation to different application requirements the many types of resins to date developed and commercially available, can be considered to satisfy a shortlist of other parameters to discriminate between the two classes "commodity" (both widely heterogeneous chemical point of view) of conventional thermosetting resins (Table 1a) and, respectively, thermosetting resins or special high-performance (Table 1b): glass transition temperature (Tg), bias ( HDT) and continuous use, hydrolytic and chemical resistance, impact resistance and adhesion to metals and minerals; reaction to fire (combustibility / flammability, smoke emission).

This "threshold" of features, beyond which lie the special resins (satisfying the needs of more demanding applications of the types listed above) is summarized as follows:

* Impact resistance and adhesion to metals, glass and ceramics:> or = to those of the best conventional epoxy + amine hardeners;

* Fire: least significant inherent flame retardancy (V1-V0 sec. UL 94). As well known, these performance requirements not only exclude entirely the entire category of unsaturated polyester resins for wider use (whether ortophtalic, isophthalic or bisphenolic), but also the most qualified vinyl-ester resins (epoxy-acrylate) standards, and overall foreclosure for special vinyl ester (epoxy-acrylate multi-functional epoxy-novolacs) and all the conventional epoxy systems and semi-conventional epoxy of bisphenol A and F homopolymerization catalysts with various tertiary amines and halides boron, epoxy resins of bisphenol A and F and epoxy-amine hardeners novolacs with liquids and carbon standards, or with dicyandiamide. Well below the standards of performance are cited other important thermosetting resins such as phenolic and amino resins, "unparalleled" resistance to fire, due to their high brittleness and poor adhesion to metals and inorganic materials in general as well (for various performance deficiencies chemical and / or thermo-mechanical) several other common resins (alkyd, furan, indene-coumarone, etc..) limited use of it to the field of conventional paints.

For the crosslinked polymeric structures containing 2-oxazolidone or jointly isocyanurate and 2-oxazolidone, from variously catalyzed polymerization of reactive systems consisting of mixtures of isocyanates and epoxy resins + / or isocyanate-functional oligomers, is recognized for many years a substantial interest industry because of their remarkable thermal and chemical stability, and the high temperatures of softening that characterize them (easily and also well above 200 ° C), as well as their cost very competitive in relation to such properties. This is well demonstrated by numerous international patents 80s and 90s of last century, claiming that the preparation and a variety of uses at high temperatures, such as adhesives, matrices of composites, cellular materials for insulation and / or acoustic protective coatings, and dielectric materials electroinsulating, etc..

Unfortunately, the vastness and complexity of the chemistry of isocyanates, epoxides, and especially of mixed systems isocyanate-epoxide inherently difficult to make rapid and reproducible generation of polymeric materials isocyanurate-oxazolidone with the chemical constitution and physical-mechanical properties desired.

In particular, the kinetics of each process is significantly affected by a multitude of very different catalytic agents or co-catalyst (intentionally introduced, present as impurities or by-products), the concentration ratios between the primary reactive species (isocyanates and epoxides) and temperature.

Most varied catalysts have been proposed and studied to date for this particular type of reactive systems: ethyl-methyl-imidazoles and other alkyl-imidazoles, quaternary phosphonium and ammonium salts, alkali metal halides and alkaline earth metals in aprotic polar solvents, complexes of Lewis acids (halides such as boron, aluminum chloride, etc..) with amines, amides or tertiary phosphines, phosphine oxides, etc.. and many catalysts typically used in the production of conventional foam polyisocyanurates as metal carboxylates alkali, alkaline earth metals, of various heavy metals and transition, amino-phenols, and others.

In general, however, the catalyst does not permit ever, or permit only if incurred in percentages then introduced very harmful to the thermo-oxidative stability and chemistry of polymeric materials final hardening time of liquid-epoxy isocyanate hybrid option adequately short (<20-30 minutes) at reasonably low temperatures (typically in the range 20-80 ° C) compatible with most current technologies for the manufacture of finished products or semifinished materials thermosets (including composites).

Many of the most active catalysts among those known and referred to preferentially promote the formation of isocyanurate rather than 2-oxazolidone, resulting in densely crosslinked materials too fragile and unacceptably, or (or in association with this effect) causing at least one of the undesirable side reactions and (3) and (4) of Scheme 3: the first (formation of carbodiimide) due to consumption of isocyanate to generate CO2 within the material (formation of micro-cavities), the second subtracts irreversibly epoxy groups to the formation of the desired groups 2-oxazolidone.

The complex has prevented critical quoted actually still reactive isocyanate-epoxy systems to play the role to which they potentially compete in the qualified field of high performance thermosets. Recently, mass-to-point efficient and selective catalytic systems, coupled with the ability to build and maintain optimal processing protocols through adequate knowledge of the peculiar chemistry of curing and its chemical and physical parameters of control, has created the ' actual availability of a class of thermosetting resins (epoxy resins, isocyanate-FPR) reliable, with surprisingly high performance thermo-mechanical properties, excellent chemical resistance and thermo-oxidative, and simultaneously highly cost competitive against high-performance resins currently available trade (see Tables 1a and 1b).

Through the specific catalyst polymerization owners FPC specially developed, the setting time of these resins at temperatures between 25 and 100 ° C is easily altered at the discretion within very broad limits, ranging from hours to minutes, and possibly underestimate up to 30 - 40 seconds at 80-100 ° C. After appropriate post-heat treatment, the resins are converted into glass completely transparent polymer insoluble in color from amber to brown, with a heat distortion temperature between 250 and 320 ° C depending on the wording.

By varying the type and concentration of catalyst and temperature, the hardening time can be adjusted to meet a wide range of processability requirements: those of the fast manufacturing of parts or composite parts molded as R-RIM, S -RIM, RTM, RTM and pultrusion-HS, those procedures or relatively slow lenses of Liquid Injection Molding, Vacuum Infusion Molding or casting forms in open or closed.

These low cost hard resins are further characterized by: 1) exceptional hydrolytic resistance, solvents and aggressive chemicals, 2) good intrinsic resistance to fire, 3) good adhesion to mineral glass, ceramics and metals, 4) low absorption water. In addition to these characteristics, their resistance to exposure to peak temperatures up to 350 ° C and continuous use temperatures up to 200 ° C and more makes them ideal materials as matrix resins for structural composites for construction of parts and components, encapsulation or coating of electrical / electromechanical / electronic, and in all those cases that require a critical combination of high performance, cost competitive and fast processability of the material.

3.2 Characteristics of processability

3.2a Pot-Life and polymerization rate Pot-life at temperatures up to 50 ° C: perfect latency (stability of the initial viscosity) adjustable from 10-15 minutes to 1-1.5 hours depending on temperature, catalyst type and concentration of FPC. Gel times at 60-100 ° C: 20 seconds to 2 hours depending on temperature, type and concentration of catalyst.

Vitrification times to 60-100 ° C: 40 seconds to 6 hours depending on temperature, type and concentration of catalyst.

Detailed investigations through mapping the evolution of dynamic-mechanical properties of resins FPR during curing under isothermal and continuous heating treatments at constant speed (processing diagrams CHT) have shown that the cycle of polymerization of these systems consists of two distinct stages, and willing, well-separable: (i) the first stage, which occurs at temperatures up to 120 ° C, provides a glassy material of yellowish and fragile, characterized by a maximum glass transition temperature (Tg1 ° ° ) of 100-120 ° C, still capable of hot forming and soluble in most common polar organic solvents, (ii) the second reaction step, which takes place at temperatures above 140 ° C leads to the final material at high point softening (up to maximum temperature of glass transition (Tg2 ° °) is completely insoluble in coloring from amber to dark amber. With low or moderate concentrations of catalyst, the curing process can therefore be discontinued at the first stage by rapid cooling , the pre-cured resin can be stored, possibly minced hot formed at a later stage and then subjected to heat treatment of complete cure. These features combined make these resins can also be used in technologies of pre-impregnation of glass fiber or carbon (for the manufacture of structural composites and Printed Circuit Boards) in this area, because of their inherently low initial viscosity, these resin systems have compared to epoxy resins, the advantage of not requiring solvents (eliminating the problems related to their subsequent removal) in the process of fiber impregnation. The only cure is required to protect the material partially reacted isocyanate-epoxide by excessive rates of atmospheric moisture during storage.

3.2b processability Microwave Thanks to their specific mode of action of catalysts, these isocyanate-epoxy resins are ideal for hardened and / or post-treatment hardened by microwave (UHF): in this way of working, the hardening time and post-curing can be minimized to 1 / 4 ÷ 1 / 10 of those cited above for conventional processing conditions. For example, the cycle of 2 hours post-curing at 180-220 ° C rolled S-RIM FPR S-1 resin reinforced with glass fibers may be replaced by a treatment of only 15 minutes under microwave heating with an average temperature of the laminates of the same 225 ° C. Catalysts recently developed specifically for microwave processing (FPC FPC W1 and W2) allow for the preparation and use of compositions of FPR resins with an exciting combination of pot life at room temperature particularly long (up to 4-6 hours) and particularly fast curing under irradiation.

3.2c Rheological properties Initial viscosity: 100 to 600 cps at 23 ° C depending on the formulation, ie (without thinners of any kind) viscosity of 5-10 times lower than those of liquid epoxy resin systems formulated with different hardeners, and at least 2-4 times lower than those of conventional unsaturated polyester resins and vinyl ester.

Chemoreologia: typical profile of "snap-curing, as required, for example, in RTM and RIM technologies

Thixotropy: the resins can easily be equipped with thixotropic properties, by adding conventional thixotropic agents (eg, 0.5 to 1% by weight of colloidal silica).

The fully reacted resins have excellent thermal stability up to 280 ° C, being able to support current continuous use temperatures> 150 ° C and typically 180 ÷ 200 ° C and peak temperatures up to 350-360 ° C. Their high-temperature aging involves both inert atmosphere and in the air, a simple and slow weight loss, without any damage or microstructural mass of the surface and it remains smooth and shiny. For example, the weight loss of specimens of pure resin is 5 to 6% after 200 hours of continuous exposure in air at 250 ° C, while that of resin reinforced with glass fiber or loaded with inert mineral powders such as flour quartz, calcined kaolin, silica, etc.. (60% by weight of fibers or mineral fillers) varies in the range 2.5 - 2.8% after 2000 hours continuously at 200 ° C even in air. For comparison, Table 4 shows the typical values of weight loss under continuous exposure to high temperatures in air for different epoxy materials for use as bonded. The data in Table 4 show an appreciable superiority FPR H resins even in respect of epoxy with anhydride hardeners, whose thermo-oxidative resistance in the long term is well recognized as optimal, and lower (under the thermosetting polymer) only to that of much more expensive and technically demanding imide resins, cyanate-and acetylene-functional.

3.3c Fire.

The hardened resins have inherent flame retardant properties (as opposed to unsaturated polyester resins, vinyl ester and epoxy-conventional), presenting a fire behavior not much different from that of phenolic resins and imide. Classification according to UL 94 (Underwriters Laboratories) for specimen thickness std. = 3.2 mm

resins with addition of 10-20% mineral flame retardants special best of V0 =

resins partially brominated = much better V0

3.3d Absorption of Water and Chemical Resistance In boiling water or in moist air saturated completely hardened resins exhibit water absorption significantly lower than those of the best epoxy hardened current (maximum water absorption equilibrium = 0.9 ÷ 1.0% by weight). The comparative data of Table 5 show the superiority of FPR resins compared to the generality of epoxy materials, and especially to those cured with DDS (the highest Tg) for structural class Aerospace (problems which hydrophilicity, hydration attitudes in moist air and consequent significant loss of stiffness, dimensional instability, etc.. are well known and critically considered in the field of structural composite materials).

With no chemical groupings hydrolytically or otherwise chemically sensitive (such as esters, amides or urethanes), the glass transition temperature and mechanical properties of cured resins are only minimally affected by aging, that is wet in hot water (even in the presence of surfactants). Because of their chemical structure, their resistance to aggressive chemicals is also excellent. Only strong acids and bases and concentrates, can attack and degrade slowly surface resins react fully (in fact capable of withstanding, for example, 12 hours immersion in aqua regia at room temperature, or at least 24 hours in caustic soda 20% hot). The comparative figures of various chemicals and hydrolytic resistance of different aggressiveness reported in Table 6 show a substantial superiority chemistry "Overall resins ISOCYANATE-EPOXY FPR compared to all epoxy materials for use as a consolidated and this superiority is" overwhelming "against unsaturated polyester resins and vinyl-ester if the comparison on the hydrolytic resistance, and above all the bases from which these materials are known to be chemically literally demolished.

3.3e Mechanical and Thermo-Mechanical Properties of Resins Pure completely polymerized The overall spectrum of their mechanical and thermo-mechanical configure these as excellent matrix resins for structural composites, especially for applications at high temperatures.

4. Main Degrees of Isocyanate-Epoxy FPR Resin Developed

4.1 Two-component resins FPR Comparing materials put at a relative humidity of 50-55%, flexural properties, tensile and impact at room temperature resins ISOCYANATE-EPOXY FPR are generally equivalent to those of the best unsaturated polyester resins, vinyl ester and epoxy conventional and special "non-impact resistant":

flexural strength at 23 ° C (ASTM D790) = 90 to 110 MPa

flexural modulus at 23 ° C (ASTM D790) = 3 to 4 GPa

A comparison of these values of mechanical properties in bending with the corresponding ranges of variability for different types of epoxy materials for current (shown in Table 7) shows an equivalent rigidity and a strict inferiority average 20% of the tensile strength of FPR compared to epoxy resins [for material conditioned at 23 ° C to dry (in a relative humidity of 50-55%)]. Because of the higher - much higher capacity for water absorption of epoxy resins compared to FPR (see Table 3.3de 5), comparative characterisations on materials to put up along 23 ° C in ambient relative humidity of 95-100% have highlighted the achievement of general equivalence of the resistance to bending and tension between the different epoxy resins for comparison and FPR, and a significant superiority of elastic modulus of the latter compared to the same epoxy reference.

As illustrated in Figure 6a, FPR completely cured resins show better retention of mechanical properties over a very wide temperature range, at least up to about 50 ° C below their glass transition temperature: decrease of 20 to 25% of modulus over the entire temperature range -50 ÷ 200-220 ° C for standard resins (resins FPR S), and over the -50 ÷ 260 ° C for those high heat distortion temperature (FPR H resins). Obviously, decreases proportionally much lower stiffness are exhibited from the same mineral fillers and additives, a fortiori, from reinforced with glass fibers or carbon.

4.2 Catalysts and Polymerization Specialists Owners FPC The FPC catalysts are insensitive to moisture, are non-toxic, harmless, non-corrosive and non-flammable, with a guaranteed minimum of one year stability at room temperature when properly stored in closed containers and protected from prolonged exposure to sunlight or sources artificial actinic light (preferably in cans or metal drums or in dark glass containers). Products, "catalyst pure" systems are only available in conjunction with FP Resin System complete. Products, "catalyst concentrate" are available separately from components isocyanate "and" epoxy "system PF Resin System users interested in their own supplies, according to the specifications of liquid isocyanates and epoxy resins for different systems PF Resin System.

6. Answers to Frequently Asked Questions The FPR resins contain plasticisers, solvents and / or volatile organic compounds? The FPR Resin Systems are specifically developed to support very high temperatures (250 - 300 ° C), similar to commercial multifunctional epoxy systems with higher glass transition temperature, for structural, electrical, electronic and electromechanical challenging, with the advantage to be compared to these, much less viscous and very quickly cured. In relation to their primary intended use as materials for high temperatures, FPR resin systems contain no plastic, paint thinner or solvent, nor any volatile organic compound.

These materials can be toughened thermosetting polymer additives with conventional toughening? FPR Resin Systems chemically toughened plastic and can be developed on demand according to specific technical requirements of the buyer, though hardened resins in this family with values of the glass transition temperature below 220 ° C are not recommended. This in order to minimize adverse effects, however toughening agents and plasticizers used against excellent heat resistance, hydrolytic, chemical and fire their own these thermosets. Several toughening agents oligomeric / polymeric use established in the field of epoxy resins can also be used in epoxy-isocyanate systems, with effects

What are the margin of tolerance on the conditions of processing / curing, for example% humidity, temperature, etc.. ? The FPR Resin Systems are much more tolerant of moisture than is commonly expected on the basis of their high content of aromatic isocyanate free starting. For the manufacture of structural composites and castings in the mold quality, pre-vacuum degassing of resins is desirable or even strongly recommended, as it is for all liquid epoxy systems used for the same purposes. Typical requirements for the manufacture of parts and quality parts and composite structural processes through closed molds (R-RIM, S-RIM, RTM, Vacuum Infusion Molding and casting): molds clean and dry, reinforcing fibers and mineral fillers having or pre-dried with hot air or infrared so you have a moisture content less than 0.05% by weight and preferably less than 0.02% (good option microwave or radio frequency drying of glass fiber); transfers resins through pipes clean and dry containers purgaggio resins with nitrogen or air dry (recommended, though not usually necessary).

What are the storage conditions of the components of the FPR Resins, p. es. % moisture, maximum temperature and duration of the products in stock? Epoxy (insensitive to humidity) of at least one year at room temperature (up to 35 ° C) in closed containers. Isocyanate (reactive with water and humidity): typical duration of isocyanates MDI liquid, that is 6 months to maximum 20 ° C in original sealed drums or containers provided partially emptied after purgaggio closed carefully with dry air or nitrogen. Catalyst FPC (moisture insensitive or only weakly hygroscopic): one year at room temperature (up to 35 ° C) in original sealed containers, at least 6 months in milk cans or partially emptied, provided always tightly closed.

The isocyanate-epoxide uncatalyzed mixtures are stable over time? The isocyanate-epoxide mixtures should be prepared in quantities required before their use, and can be stored only for limited periods of time without significant increases spontaneous viscosity. Storage time at room temperature for mixtures suggested uncatalyzed epoxy-isocyanate: 48 hours maximum (typically no more than 36 hours at 20-25 ° C, no more than 12 hours at 30-35 ° C).